Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934473AbcCIXPU (ORCPT ); Wed, 9 Mar 2016 18:15:20 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:40524 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934454AbcCIXPN (ORCPT ); Wed, 9 Mar 2016 18:15:13 -0500 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Tejun Heo , Mike Galbraith , Henrique de Moraes Holschuh , Daniel Bilik , Jan Kara , Shaohua Li , Sasha Levin , Ben Hutchings , Thomas Gleixner , Jiri Slaby , Michal Hocko , Kamal Mostafa Subject: [PATCH 3.13.y-ckt 002/138] Revert "workqueue: make sure delayed work run in local cpu" Date: Wed, 9 Mar 2016 15:12:09 -0800 Message-Id: <1457565265-15195-3-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1457565265-15195-1-git-send-email-kamal@canonical.com> References: <1457565265-15195-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.13 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3056 Lines: 77 3.13.11-ckt36 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Tejun Heo commit 041bd12e272c53a35c54c13875839bcb98c999ce upstream. This reverts commit 874bbfe600a660cba9c776b3957b1ce393151b76. Workqueue used to implicity guarantee that work items queued without explicit CPU specified are put on the local CPU. Recent changes in timer broke the guarantee and led to vmstat breakage which was fixed by 176bed1de5bf ("vmstat: explicitly schedule per-cpu work on the CPU we need it to run on"). vmstat is the most likely to expose the issue and it's quite possible that there are other similar problems which are a lot more difficult to trigger. As a preventive measure, 874bbfe600a6 ("workqueue: make sure delayed work run in local cpu") was applied to restore the local CPU guarnatee. Unfortunately, the change exposed a bug in timer code which got fixed by 22b886dd1018 ("timers: Use proper base migration in add_timer_on()"). Due to code restructuring, the commit couldn't be backported beyond certain point and stable kernels which only had 874bbfe600a6 started crashing. The local CPU guarantee was accidental more than anything else and we want to get rid of it anyway. As, with the vmstat case fixed, 874bbfe600a6 is causing more problems than it's fixing, it has been decided to take the chance and officially break the guarantee by reverting the commit. A debug feature will be added to force foreign CPU assignment to expose cases relying on the guarantee and fixes for the individual cases will be backported to stable as necessary. Signed-off-by: Tejun Heo Fixes: 874bbfe600a6 ("workqueue: make sure delayed work run in local cpu") Link: http://lkml.kernel.org/g/20160120211926.GJ10810@quack.suse.cz Cc: Mike Galbraith Cc: Henrique de Moraes Holschuh Cc: Daniel Bilik Cc: Jan Kara Cc: Shaohua Li Cc: Sasha Levin Cc: Ben Hutchings Cc: Thomas Gleixner Cc: Daniel Bilik Cc: Jiri Slaby Cc: Michal Hocko Signed-off-by: Kamal Mostafa --- kernel/workqueue.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index dcae810..eb1cc22 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1475,13 +1475,13 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq, timer_stats_timer_set_start_info(&dwork->timer); dwork->wq = wq; - /* timer isn't guaranteed to run in this cpu, record earlier */ - if (cpu == WORK_CPU_UNBOUND) - cpu = raw_smp_processor_id(); dwork->cpu = cpu; timer->expires = jiffies + delay; - add_timer_on(timer, cpu); + if (unlikely(cpu != WORK_CPU_UNBOUND)) + add_timer_on(timer, cpu); + else + add_timer(timer); } /** -- 2.7.0